Backfire arrester and flash back preventer



Aug. 17, 1948. M. OLSON ET AL BACKFIRE ARRESTER AND FLASHBACK PREVENTER 2 Sheets-Sheet 1 Filed Jan. 15, 1944 INVENTO s MALVEN L.OLSON ELWOO A. BERGER ATTO R N EY Aug. 17, 1948. M. L. OLSON ET AL 2,447,035

BACKFIRE ARRESTER AND FLASHBACK PREVENTER Filed Jan. 15,1944 2 Sheets-Sheet 2 mmm Fina II'IIIM 'l llllll I INVENTORS MALVEN LGOLSON ELWOO A.BERGER ATTORNEY Patented Aug. 17, 1948 BACKFIRE ARRESTER AND FLASH BACK PREVENTER Malven L. Olson and Elwood A. Berger, Indianapolis, Ind, assignors to Union Carbide and Carbon Corporation, a corporation of New York Application'January 15, 1944, Serial No. 518,422

1 6 Claims. This invention relates to backfire arresters which also prevent flashback and are gas mixers for blowpipes, and more particularly to arresters and mixers which utilizea porous element as the flash arresting and mixing agent.

With such porous arresters, it has been found that the porous element is liable to burn away in a small localized area facing the entrance to the as outlet passage of the arrester after a series of backfires. As, a result, the porous element is soon punctured and must be replaced.

While liquid cooling arrangements have been used to prevent undue heating, such arrangements are space-consuming and do not nicely nest with one another, when a plurality of blowpipes containing such arresters are grouped together as in a desurfacing machine. Furthermore, liquid cooling can. not be practically applied to arresters of the porous type where the failure results from concentrated impingement of flame upon a small surface area of the porous element.

Further, where the arrester element serves finally to mix the gases, little consideration has been given in the past to means for preliminarily mixing and conducting the gases to the upstream face of the porous element, prior to their entry into the pores of the element for their final mixing.

arrester in which the porous arresting element is resistant to puncture in use; a combined porous type gas mixer and backfire arrester assembly with a novel arrangement of the gas inlets in the casing for preliminarily mixing and distributing the gases across the upstream face of the porous element prior to their entry and passage through the porous element; and a backfire arrester which does not need to be water cooled and which may be nested with similar arresters when several blowpipes comprising such arresters are grouped together.

According to the present invention, a porous element may be provided with a solid metal or nonporous deflector in its downstream face in the area which is aligned with the outlet passage in the flash arrester casing. Flame flashing in firing (exploding) back through the outlet passage and striking the solid metal deflector is dispersed laterally and distributed over a large portionof the face of the porous element. The deflector thus receives the brunt of the shock of the backfire and prevents localized heating and destruction of the porous material. The casing of the arrester is so formed that it can be nested with The principal objects of the present invention I are to provide an improved porous type backfire similar arr-ester casings for space economy. Combustion supporting gas passage and a combustible gas inlet passage both discharge into a space provided in the casing adjacent the upstream face of the porous element at locations offset with respect to the deflector. In the case of the combined mixer and arrester assembly, two inlet pipes for the separate gases project into a circular mixing space. Each inlet pipe has a radially extending discharge passage and the gases, such as acetylene and oxygen, are directed together across the upstream face of the porous element. The gases are given a swirling circular motion. Thorough mixing results from the motion of the gases and passage through the porous element. The porous element also serves as a backfire arrester in which most of the downstream face of the disc is available to assist in arresting a backfire flame while the small space and high gas velocity prevents flashback continuing after a backfire.

For other objects and a better understanding of the invention, reference may be had to the following detailed description taken in connection with the accompanying drawing, in which:

Fig. 1 is a side elevational view of a blowpipe desurfacing machine utilizing a backfire arrester embodying features of the present invention;

Fig. 2 is a front view, showing the nested relation of the arresters nested together;

Fig. 3 is an enlarged cross-sectional view of an arrester, taken on line 3-3 of Fig. 1;

Fig. 4 is a fragmentary sectional view of the backfire arrester with portions of the casing and of the porous element broken away to show the inner side of the arrester, taken generally on line 1-5 of Fig. 3;

Fig. 5 is a side view, partlyin section, of a blowpipe provided with a combined gas mixer and backfire arrester assembly exemplifyin the in-- vention;

Fig. 6 is a cross-sectional view of the combined I gas mixer and arrester assembly, taken generally on line 6-6 of Fig. 5; and,

Fig. '7 is a. fragmentary detail view, partly in section, of the end of a gas inlet pipe associated with the combined mixer and arrester assembly.

Referring to Figs. 1 and 2, there is shown a plurality of nested uniform blowpipes III, H, I! and I3, each of which comprises a. backfire arrester ll, 9. conventional equal (medium) pressure type gas mixer l5, and a nozzle block is A nozzle I1 is removably secured to the block l6 by a coupling sleeve l8. The flash arrester M has an inlet portion l9 connected by pipe coupling means 2| to an elongated mixed gas pipe 22 of the conventional mixer l 5, and an outlet portion 23 connected to the nozzle block l6 by pipe coupling means 24. The pipe coupling means 24 has threaded fittings 25 and 26 connected respectively to the nozzle block 16 and the arrester 14. By having the various parts separable, they may be quickly and easily disassembled, cleaned and re- "assembled; the downtime of the machine bein thereby kept to a minimum, v

Since the arrester I4 is located downstream with respect to the mixer l5, and the mixer is thus invulnerable to carbon deposition resulting from a backflash or backfire, there is less need for the coupling means 2| between the mixer l and the flash arrester to be detachable. Only parts downstream with respect to the flash arrester l4 need to be detachable for cleaning. Pipes 21 and 28 respectively feed the separate gases to the mixer 15.

Each blowpipe has a pipe 29 for delivering cutting oxygen gas to the nozzle block 16 and to a central relatively flat discharge port 3| in the tip of nozzle [1. Each nozzle tip is also provided with a series of premixed preheating gas discharge ports. 32 which surround the cutting oxygen port 3|. Such gas jets, when ignited, produce oxy-acetylene preheating flames.

Inlet and outlet portions 19 and 23 are located respectively at opposite sides of the arrester casing. By having such portions so cated, the arrester casings of the blowpipes can be readily nested with one another, as shown, to provide the desurfacing machine with as many blowpipes as may be necessary to'thermochemically condition a ferrous metal body of a given width in a single pass.

Referring now to Figs. 3 and 4, it will be noted that the arrester casing is made in two parts, 33

and 34. Inlet portion I9 is located on the part 33. A disc-like porous element 35 is seated in a washer-shaped peripheral retainer 36 and the combination is disposed between the parts 33, and 34. This washer-shaped retainer 36 is preferably made of gas sealing material and has an inwardly radially-extending flange 31 which extends over an annular portion of the upstream face of the porous element 35. As the two parts are brought together by clamping screws .38, the peripheral portion of porous element 35 is sealed within the casing in a gas-tight manner, whereby all gas entering the inlet I 9 in order to arrive at the outlet 23 must pass through the porous element.

The porous element is made of sintered material such as that sold under the trade-mark Poi-ex. This material is formed by sintering bronze particles and compressing the sintered mass to give a porosity such as will function as a flashback arresting material yet accommodate the flow of the gases therethrough.

An inlet passage 39 enters space 4| adjacent the upstream face 42 of the poro element 35. An outlet passage 43 leads out of a narrow frusto-conically shaped space 44 provided in part 34 adjacent the downstream face 45 of the porous element 35. It is from this passage 43 that flames resulting from any backfire are directed against the element 35. The flame arriving at this passage is very hot and under high pressure and with the occurrence of the backfire bein frequent, a small portion of the pores of the porous element in the area adjacent the passage 43 have heretofore become quickly destroyed and replacement of the porous element made'neces-,.

sary. In order to protect the porous element in together.

. receives the brunt of the shock of a backfire.

When the flow of gas is in suificient volume, the narrow space 44 causes the gas to sweep across the face 45 precluding a sustained flashback flame existing there. As shown in Figs. 1 to 4 the inlet passage is brought to the upstream face of the porous metal disc at a distance offset from the disc axis and the outlet passage to allow clearance for several such backfire arresters to be placed close together coaxially, i. e., side by side and in nested relation, as shown in Fig. 2. Almost the entire upstream face of the porous disc is exposed to receive the incoming gases and assist in mixing them within the disc pores.

In Figs. 5, 6 and 7, there is shown a form of the invention in which the porous element serves not only to arrest a backfire but to mix further the mixed gases which pass through the porous element. The pipes for the separate gases, instead of being connected to a conventional mixer as in the previously described modification of the invention, are connected directly to the arrester casing. Gas streams are directed into a space overlying the upstream face of the porous element in such a manner as to give to the gases a swirling. circular motion. In other words, a combined gas mixer and arrester assembly replaces the conventional gas mixer l5 and arrester l4 of the blowpipes shown in Figs. 1 and 2.

A combined gas mixer and arrester assembly 5| is connected directly to a nozzle block 52 by a pipe 53 and has a nozzle 54 held in the nozzle block by a retaining sleeve 55. The assembly comprises two separable plates 56 and 51 clamped together by bolts 58, and a washer-shaped element 59 in which the periphery of a porous element 6i is seated. Such porous element 6|,

which may be of sintered bronze, has pores 'interconnected with one another such that portions of thegas traversing one pore are interchanged for portions of the gas traversing other pores. A solid metal or nonporous deflector 62 may be associated with the porous element 6| to lie opposite an opening 63 in plate 51 and the end of passage 63 of the pipe 53 which is screwed into a socket in the plate 51. of a backfire may then be received by the metal deflector 62, and any flame may be deflected over a large portion of the downstream face of the porous element. Such flame may be conveyed to the passage 63 by the gas which sweeps over such face if a sufficiently high velocity of the gas is attained as it flows toward the central outlet 63.

The washer-shaped retainer 59 has a radially inwardly extending flange 64 of suitable thickness to provide a gas mixing space 65 between the porous element and the internal surface of the plate 56 when the plates 56 and 51 are clamped This space 65 may be of cylindrical shape and is of suflicient depth to permit the insertion of end portions of gas supply pipes 66 and 61. The pipes 66 and 61 are threaded into suitable holes in plate 56 and have on their inner ends a nozzle 68 having an axially extending passage 69 and a radially extending passage 1|, whereby the gas leaving the nozzle 68 is-directed radially from the pipe end and across the upstream face of the porous element.

Both of the pipes 66 and 61 enter the circular The brunt of the shock.

space 63 at a location ofi'set with respect to-the center of porous element 8i and with respect to disc downstream porous face is adapted to contact any backfire flame but said space is too shallow to support continued burning of flashsages H is such as to give the gases a swirling and circular motion within circular space 65. The stream of gas issuing from the pipe 67 intersects the stream of gas issuing from pipe 88. Both gases take the circular motion, indicated by arrow 72. In this way preliminary mixing of the fuel and oxidizing gases is accomplished immediately prior to the entry of the mixed gases to the porous element Bl. The final mixing of the gases is accomplished within the porous element at.

It is thus apparent that there is provided a combined gas mixer and flash arrester assembly with an efficient preliminary mixing arrangement for the gases immediately prior to their entry into the porous element wherein th gases enter the casing from a location ofi'set with respect to the center of the porous element and to the deflector, By having a preliminary mixing arrangement within the arrester casing, a porous element of such minimum thickness as will extinguish backfires is sumcient to effect final mixing of the gases.

It is also apparent that there is provided a backfire arrester in which the porous element is protected against sustained flashbacks near it as well as backfire. The sweeping action of the gas flowing across the downstream face of the porous element toward the outlet, tends to keep such face swept clean of any carbon particles resulting from backfires. downstream side of the porous element is small enough not to sustain any flashback flame with the result that no such flashback flame is permitted after a backfire. The velocity of the gas on th downstream side of the arrester assists in preventing any slow burning backflash flame. As is well known in the art bronze is a fairly good heat conductor so that the heat of a backfire flame is distributed'through the porous mass thereby avoiding local overheated portions which might be incapable of chilling and quenching a backfire flame. The function of the porous element as a gas mixer is due to the pores being tortuous and interconnected rather than straight. Such pores also exert a better quenching action on a backfire flame than straight lin pores should be expected to do.

While various changes may be made in the detailed construction, it shall be understood that these changes shall be within the spirit and scope of the present invention as defined by the appended claims.

What is claimed is:

1. In a backfire arrester comprising a porous metal disc having multitudinous tortuous interconnected pores formed between sintered particles, a casing enclosing said disc, gas tight packing between the casing and the perimeter of the disc, a gas supply passage leading to a space within the casing adjacent the upstream face of said disc, at least the major portion of the upstream face of said disc being exposed to receive incoming gas for passage through the pores of the disc..

an outlet passage from the casing opposite the downstream face of said disc. the casing providmg a shallow space adlacent t downstream 7 sages, a porous sintered metal backfire arresting The space in the casing on the back after backfire, and the combination therewith of the improvement for enhancing the ability of said disc to withstand batkfire which improvement comprises a metal member which is non-porous to a backfire flame, embedded in the porous disc, supported thereby, and located opposite the outlet passage from -the caing in a central portion of the porous metal disc to receive the-impact of any backfire flame and spread the same over the downstream face of the porous disc whereby any backfire flame may be quenched as it is divided into numerous parts to enter and be bent within the tortuous pores of said-disc, said metal member having a surface substantially flush with the downstream face of the porous disc exposed to a, backfire flame and being at least about as large as the area of cross section of the outlet passage opposite thereto.

2. In a backfire arrester comprising a porous metal disc having multitudinous tortuous interconnected pores formed between sintered particles, a casing enclosing said disc, gas tight packing between the casing and the perimeter of said disc, a gas supply passage leading to a space within the casing adjacent the upstream face of said disc, at least the major portion of the upstream.

a shallow space adjacent the downstream face of the disc whereby the major portion of the disc downstream porous face is adapted to contact' any backfire flame but said space is too shallow to support continued burning or flashback after backfire, and the combination therewith of the improvement whereby a plurality of such arresters may be closely nested substantially coaxially, said improvement comprising a substantially right angled bend in each of the supply and outlet passages close to the casing with said passages beyond said bend extending in a direction generally parallel to the disc but in widely sepa-' rated directions angularly and the inletpassage being connected to the casing offset from the disc axis away from the direction in which the outlet passage extends from the casing beyond its bend.

3. The-combination of a casing having a gas inlet and a gas outlet, and a combined gas mixer and backfire arrester within said casing between said inlet and said outlet, said combined mixer and arrester comprising a porous metal disc coaxial with said outlet and having its faces respectively spaced from opposite walls of said casing to provide gas spaces respectively directly adjacent and communicating with the open ends of pores in the upstream and the downstream faces of said disc, and a non-porous metal member I secured to the center portion of said disc and having a surface whose area is greater than the cross-sectional .area of said outlet, said surface being arranged directly and axially opposite said outlet and to assist in quenching such flame bydeflecting and spreading the saline radially into the space adjacent the downstream face of said disc.

4. A porous backfire arrester and gas mixer comprising a casing having inlet and outlet pasface of the disc where the major portion of the 7 element retained in the casing in axial alignment with the outlet passage thereof, said element having tortuous interconnected pores with heat conductive walls, said casing providing a narrower space between the porous element and the outlet passage than between said eleemnt and the inlet passage, a deflector of non-porous metal disposed on the downstream face of the porous element in a central portion thereof adjacent to and in axial alignment with the outlet passage to receive the shock of a backfire flame entering said space between the porous element and the outlet passage, said metal deflector member having its outer surface substantially flush with the downstream face of the porous surface and having an area at least as large as that of a cross section of the outlet passage opposite thereto, and said inlet passage entering the space between the casing and porous element at a position oifset with respect to the axis of the porous member.

5. A porous backfire arrester comprising a casing having two separate gas inlet passages and a mixed gas outlet passage, a porous element having pores in which any flame resulting from backfire is arrested, means for gas tightly securing the porous'element within the casing between the inlet passages and the outlet passage to confine the path of gases from the inlet passages to the porous element, said casing providing a space adjacent the upstream face of the porous element, the two gas inlet passages leading into said space on the upstream face of the porous element and being so directed as to project the streams of gas' therethrough parallel to the face of said disc and as to convey such streams at an acute angle in said space.

6. The combination with a porous sintered metal backfire arrester element, of a casing enclosing said element, a supply passage leading into the casing adjacent the upstream i ace of said element, an outlet passage leading from the casing 8 adjacent the downstream face of said element, a nonporous deflector member secured to the downstream face'of said element in a central portion thereof, said deflector member having an area at least as large as the cross sectional area of the outlet passage opposlte'thereto and in substantial alignment with the outlet passage leading from the casing whereby any backfire flame impinges upon said deflector member and is spread radially outward to be arrested in the pores of said element.

MALVEN L. OLSON.

ELWOOD A. BERGER.

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